The invention concerns spinal osteosynthesis systems, in particular for anterior fixation.
The document FR-2,731,344 discloses a spinal osteosynthesis system comprising a rod, a vertebral screw having a body to be anchored in a vertebra, and a head in the form of a threaded rod. The system comprises a connector with two branches which can be engaged on the screw head. A clamping nut can be fitted on the screw head in order to clamp the two branches between the base of the screw head and the nut. The rod engaged between the branches is thus clamped and immobilized.
This system has many advantages. As it includes a small number of components and is easy to put in place, it permits rapid fitting during a surgical intervention. However, the nut has a hexagonal outer profile which is necessary to permit its maneuvering and its clamping by means of a socket wrench. Now, such a profile generates numerous sharp edges and projecting corners capable of damaging the body tissues coming into contact with the nut. Similarly, it is difficult to prevent a threaded end part of the screw head from protruding from the nut upon completion of clamping. Now, this thread itself also presents projecting edges which can be damaging to the body.
An object of the invention is to reduce the number of parts projecting from the system once this has been fitted.
To achieve this object, the invention provides a spinal osteosynthesis system, in particular for anterior fixation, comprising:
an elongate connection element;
a vertebral screw having a threaded head;
a connector including two branches which can be fitted on the screw and can clamp the connection element between them; and
a threaded clamping member which can cooperate with the head in order to clamp the branches, in which the head has a threaded orifice, the clamping member comprising a threaded rod which can engage with the orifice.
Thus, the thread of the vertebral screw extends in an orifice, and the threaded orifice of the screw is closed off by the clamping member once fitting has been completed. Therefore, contact with the patient""s body is no longer possible with the thread of the vertebral screw. Moreover, as the clamping member is a male piece, it is possible to form a maneuvering recess therein of polygonal profile intended to cooperate with a male instrument for maneuvering the clamping member and thereby dispense with the outer edges. This therefore also reduces the number of parts projecting from the clamping member. In addition, the connector is engaged on the head of the vertebral screw without interfering with a thread thereof. Its wedging is thus better, even before clamping by the clamping member. The connector can thus be positioned in advance on the vertebral screw in a reliable manner.
Advantageously, the clamping member has a recess of polygonal profile along a longitudinal axis of the member.
Advantageously, the clamping member comprises a head having a spherical and convex lower face, one of the said branches of the connector having a spherical and concave upper face which can be in contact with the convex face upon clamping of the branches.
It is thus possible to control the relative angular position of the connector and of the vertebral screw which is rigidly fixed to the clamping member.
Advantageously, the orifice of the vertebral screw has a recess of polygonal profile along a longitudinal axis of the screw.
This recess too, permitting maneuvering of the vertebral screw, reduces the number of projecting parts.
Advantageously, the recess extends in the thread of the orifice.
Thus, despite the presence of the thread and of the recess, it is possible for the head of the vertebral screw, and thus the system, to be given reduced dimensions.
Advantageously, the profile of the recess of the vertebral screw and the profile of the recess of the clamping member have the same shape and the same dimensions.
It is thus possible to maneuver the vertebral screw and the clamping member using one and the same male instrument, thereby reducing the equipment needed for the surgical intervention and reducing the risk of error in the choice of instruments.
Advantageously, the head of the vertebral screw has a lateral face with a smooth outer end.
Advantageously, the system comprises a second vertebral screw, one of said branches having an extension which can be engaged on the second screw.
Thus, fixation of the connector to the vertebra by means of the two screws ensures precise, stable and reliable positioning of the connector and thus of the connection element.
Advantageously, the system comprises a second elongate connection element, the connector being able to be fixed simultaneously to the two connection elements.
Thus, the presence of the two connection elements gives the system very great rigidity, without complicating its assembly, without increasing the volume of its various components (which renders it compatible with fitting via the endoscopic route), and while maintaining if need be the possibility of controlling the angular position of the connector relative to the first connection element. The system according to the invention does not require identical bending on the two connection elements. Moreover, the number of connectors can remain small.
The system according to the invention can be put into place via the endoscopic route and is designed to be fixed in the anterior position.